The present disclosure relates generally to a power controllers and related power supply control methods, especially to automatic compensation to inductance variation of an inductive device in a power supply.
Electronic devices usually need a power supply capable of providing a power source with output ratings such as maximum output current, maximum output voltage, or maximum output power. Switching-mode power supplies (SMPS), due to excellent conversion rate, simple topology, and compact product size, are popularly adapted by electronic apparatuses.
A power supply, if properly designed, needs protection mechanism to avoid risk from happening due to accident or disoperation. For instance, protection mechanism could include over temperature protection (OTP), over voltage protection (OVP), over current protection OCP), over power protection (OPP), output short protection (OSP), and so forth. OTP refers to the protection provided when the temperature of a power supply is over high. OVP deals with the operation when the output voltage of a power supply exceeds a limit. OCP and OPP limit the output current and the output power of a power supply to be under designed ratings. OSP involves the protection when an output voltage of a power supply is clamped to be 0V.
The implementation of OCP or OPP of a SMPS normally relies on the detection of a winding current through an inductive device in the SMPS. FIG. 1 demonstrates the waveform of a current-sense signal VCS generated by sensing a winding current of an inductive device in a SMPS. In view of OCP and OPP, the current-sense signal VCS is expected to be limited under a signal VCS-LIMIT, which might be a predetermined value or a variable depending on a compensation voltage reflecting a load of a SMPS. In reality, signal propagation delay could cause nevertheless a peak VCS-PEAK of the current-sense signal VCS much higher than the signal VCS-LIMIT, as shown in FIG. 1. A time delay TD occurs for a circuit to conclude an ON time TON of a power switch after finding that the current-sense signal VCS exceeds the signal VCS-LIMIT, and the current-sense signal VCS, due to its inertia, still goes upward during this time delay TD. Therefore, the peak VCS-PEAK finally resulted is different from the signal VCS-LIMIT by a gap ΔVCS, whose magnitude depends on the value of an input voltage of the SMPS, the inductance of the inductive device, and the time delay TD. Inductance variation of the inductive device, even though allowable or tolerable in mass production, could generate different peaks VCS-PEAK, and easily cause inaccuracy or uncertainty to the conditions for triggering OCP and OPP.